P2558PDE4 regulates cardiac pacemaker function

2019 ◽  
Vol 40 (Supplement_1) ◽  
Author(s):  
D Mika ◽  
A M Gomez ◽  
R Fischmeister ◽  
G Vandecasteele
Keyword(s):  
Cardiac Pacemaker ◽  
Hydrolytic Activity ◽  
Pde4 Inhibitor ◽  
Pacemaker Activity ◽  
Ventricular Cells ◽  
Pacemaker Function ◽  
S 100 ◽  
Beating Rate ◽  
Respective Contribution

Abstract Background Numerous epidemiological and clinical studies have revealed a positive correlation between heart rate (HR) and cardiovascular morbimortality. The autonomic nervous system is the major extracardiac determinant of HR. During sympathetic stimulation, the activation of β-adrenergic receptors (βAR) induces an increase in cAMP levels, leading to positive chronotropic effect. Among the 5 cardiac cAMP-PDE families, PDE4 is critical for controlling excitation-contraction coupling (ECC) during βAR stimulation in atrial and ventricular cells. PDE4 may also be important for automaticity. 3 genes encode for PDE4s: pde4a, pde4b, pde4d. Their respective contribution to the regulation of pacemaker activity remains ill-defined. Purpose Define the role of PDE4 isoforms in the regulation of cardiac pacemaker activity Methods Total PDE activity was determined in mouse sinoatrial node (SAN) tissue as the cAMP-hydrolytic activity measured in the absence of PDE inhibitor and the fraction corresponding to PDE4 activity was assessed by including the PDE4 inhibitor Ro-20-1724. The in vitro pacemaker activity was assessed by measuring spontaneous Ca2+ transients in Fluo4-loaded-SAN tissue. Images were obtained using confocal microscopy. Results Ro-20-1724 increased beating rate of intact SAN and increased PKA-phosphorylation of key ECC actors (ryanodine receptor, phospholamban and contractile proteins). PDE4 activity was found to account for 60% of the total cAMP-PDE activity in SAN (n=3 independent experiments). PDE4A, PDE4B and PDE4D isoforms were found to be expressed in mouse SAN (n=5 independent experiments). In PDE4D-, but not in PDE4B-deficient mice, Ca2+ homeostasis was altered in control conditions (ctrl) and after βAR stimulation with isoprenaline (iso). Indeed, ablation of PDE4D induced decreased beating rate (ctrl: 1.00±0.08 s–1 vs 1.57±0.05 s–1; iso: 1.71±0.17 s–1 vs 2.39±0.08 s–1, p<0.0001) and increased Ca2+ spark frequency (ctrl: 15.9±5.2 sparks/s/100 μm vs 1.9±0.4 sparks/s/100 μm; iso: 22.9±7.1 sparks/s/100 μm vs 0.6±0.2 sparks/s/100 μm, p<0.0001) (Figure). Calcium Homeostasis in SAN cells Conclusion PDE4 controls pacemaker function in mice and PDE4D ablation strongly perturbs normal SAN activity. Acknowledgement/Funding ANR, Fondation Lefoulon Delalande, CORDDIM

PDE4B and PDE4D differentially regulate cardiac pacemaker activity

EP Europace ◽  
2021 ◽  
Vol 23 (Supplement_3) ◽  
Author(s):  
WPV Pereira De Vasconcelos ◽  
AMG Gomez ◽  
RF Fischmeister ◽  
GV Vandecasteele ◽  
DM Mika
Keyword(s):  
Ventricular Myocytes ◽  
Cardiac Pacemaker ◽  
Hydrolytic Activity ◽  
Pde4 Inhibitor ◽  
Pacemaker Activity ◽  
National Budget ◽  
Beating Rate ◽  
Public Grant

Abstract Funding Acknowledgements Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Agence Nationale de la Recherche (ANR) Background Heart rate (HR) is generated by spontaneous electrical activity in the sinoatrial node (SAN) and is modulated by the autonomic nervous system. During sympathetic stimulation, the activation of β-adrenergic receptors (βAR) increases cAMP levels, leading to positive chronotropic effect. Among the 6 cardiac cAMP-PDE families, PDE4 is critical for controlling excitation-contraction coupling (ECC) during β-stimulation in atrial and ventricular myocytes. PDE4 may also be important for automaticity. 3 genes encode for PDE4 in the heart (pde4a, 4b, 4d). We propose to investigate their respective contribution to the regulation of pacemaker activity.  Methods Total PDE activity in mouse SAN was determined as the cAMP-hydrolytic activity measured in the absence of PDE inhibitor and the fraction corresponding to PDE4 activity was assessed by including the PDE4 inhibitor Ro-20-1724. The in vitro pacemaker activity was assessed by measuring spontaneous Ca2+ transients in Fluo4-loaded-SAN tissue from wild-type (WT) and PDE4KO mice. Images were obtained using confocal microscopy. Telemetry EKG was recorded in conscious mice in control (CTRL) conditions, after pharmacological denervation with atropine (1 mg/kg) and propranolol (2 mg/kg) and after β-stimulation with isoproterenol (ISO, 1.5 mg/kg). HR variability was evaluated by calculating the SDNN (standard deviation of RR intervals) parameter. Results Ro-20-1724 (10 µM) increased beating rate of intact SAN and increased PKA-phosphorylation of key ECC actors (ryanodine receptor, phospholamban and contractile proteins). PDE4 activity was found to account for 60% of total cAMP-PDE activity in SAN. PDE4A, 4B and 4D isoforms were found to be expressed in mouse SAN. In PDE4BKO SAN, the effect of ISO on SAN beating rate was higher than in WT. Ablation of PDE4D induced decreased beating rate in CTRL and ISO conditions and increased Ca2+ spark frequency compared to WT SAN. In vivo, PDE4BKO and PDE4DKO mice displayed increased resting HR during day and night. HR variability was decreased in PDE4BKO, but not in PDE4DKO mice during the day, and decreased in both genotypes at night compared to WT mice. After atropine + propranolol denervation, the rhythmic phenotype was only maintained in PDE4BKO but not in PDE4DKO mice. The response to β-AR stimulation with ISO was higher in PDE4BKO than in PDE4DKO. In addition, under ISO we observed an increased number of premature beats and atrioventricular blocks in PDE4DKO, but not in PDE4BKO mice. Conclusion PDE4B and PDE4D differentially regulate cardiac pacemaker activity. While PDE4B clearly controls intrinsic SAN automaticity, PDE4D might be important for ANS-mediated regulation of HR and conduction.

scholarly journals The effect of temperature on spontaneous action potential discharge of the isolated sinus venosus from winter and summer plaice (Pleuronectes platessa)

1995 ◽  
Vol 198 (1) ◽  
pp. 137-140 ◽  
Author(s):  
A A Harper ◽  
I P Newton ◽  
P W Watt
Keyword(s):  
Action Potential ◽  
Discharge Rate ◽  
Cardiac Pacemaker ◽  
Intrinsic Rate ◽  
Effect Of Temperature ◽  
Pacemaker Activity ◽  
Duration Of Action ◽  
Diastolic Depolarization ◽  
Significant Difference

The spontaneous cardiac pacemaker activity and conformation were recorded in vitro, using intracellular recording methods, from heart tissue of summer- and winter-caught plaice. The effects of changing temperature on the pacemaker rate, duration of action potential and diastolic depolarization were investigated by altering the temperature of the superfusing medium. The resting intrinsic rate of discharge was significantly greater in pacemaker cells from winter plaice (P=0.05), but there was no significant difference between winter and summer fish in the apparent Arrhenius activation energies for this process. However, there was a significant difference in the estimated intercept, indicating a thermal shift in the processes underlying the spontaneous pacemaker rhythm. There was no significant difference in the diastolic depolarization duration recorded from winter and summer fish over the temperature range 4&shy;22 &deg;C. The major effect of previous environmental temperature was on the duration of the action potential (P&lt;0.02), indicating that the observed changes in pacemaker discharge rate were not influenced by the processes that determine the duration of the pacemaker diastolic depolarisation but were modulated by the channel events that give rise to the action potential.

Calcium Sensitizers Isolated from the Edible Pine Mushroom, Tricholoma matsutake (S. Ito & Imai) Sing

2013 ◽  
Vol 68 (3-4) ◽  
pp. 113-117
Author(s):  
Yunlong Hou ◽  
Shichao Sun ◽  
Lijun Wu ◽  
Xiaodan Wang ◽  
Ting Li ◽  
...  
Keyword(s):  
Ex Vivo ◽  
Edible Mushroom ◽  
Ion Concentration ◽  
Screening Tests ◽  
Tricholoma Matsutake ◽  
Inotropic Effects ◽  
Ventricular Cells ◽  
Calcium Sensitizers ◽  
Beating Rate

1 Three lactam compounds were isolated from the fruiting body of Tricholoma matsutake (S. Ito & Imai) Sing., an edible mushroom, and their structures were identifi ed as cyclo- S-proline-R-leucine (), hexahydro-2H-azepin-2-one (2), and butyl 5-oxo-2-pyrrolidine carboxylate (3) by chemical, physicochemical, and spectral evidence. In in vitro screening tests, compounds 1 and 2 acted as calcium sensitizers in ventricular cells from rat. Further studies on compounds 1 and 2 in ex vivo isolated right atria showed positive inotropic effects without disturbing the spontaneous beating rate. The inotropic effect of compounds 1 and 2 could be greatly abolished by pretreating the myocardium in Ca2+-free solution. These fi ndings indicate that compounds 1 and 2 can signifi cantly increase the calcium ion concentration ([Ca2+]i) in myocytes, which is greatly dependent on the infl ux of extracellular Ca2+.

scholarly journals Dual Activation of Phosphodiesterase 3 and 4 Regulates Basal Cardiac Pacemaker Function and Beyond

2021 ◽  
Vol 22 (16) ◽  
pp. 8414
Author(s):  
Tatiana M. Vinogradova ◽  
Edward G. Lakatta
Keyword(s):  
Cardiac Pacemaker ◽  
Adenylyl Cyclases ◽  
Camp Production ◽  
Sa Node ◽  
Phosphodiesterase 3 ◽  
Pacemaker Function ◽  
Dependent Protein ◽  
Beating Rate ◽  
Dual Activation ◽  
High Level

The sinoatrial (SA) node is the physiological pacemaker of the heart, and resting heart rate in humans is a well-known risk factor for cardiovascular disease and mortality. Consequently, the mechanisms of initiating and regulating the normal spontaneous SA node beating rate are of vital importance. Spontaneous firing of the SA node is generated within sinoatrial nodal cells (SANC), which is regulated by the coupled-clock pacemaker system. Normal spontaneous beating of SANC is driven by a high level of cAMP-mediated PKA-dependent protein phosphorylation, which rely on the balance between high basal cAMP production by adenylyl cyclases and high basal cAMP degradation by cyclic nucleotide phosphodiesterases (PDEs). This diverse class of enzymes includes 11 families and PDE3 and PDE4 families dominate in both the SA node and cardiac myocardium, degrading cAMP and, consequently, regulating basal cardiac pacemaker function and excitation-contraction coupling. In this review, we will demonstrate similarities between expression, distribution, and colocalization of various PDE subtypes in SANC and cardiac myocytes of different species, including humans, focusing on PDE3 and PDE4. Here, we will describe specific targets of the coupled-clock pacemaker system modulated by dual PDE3 + PDE4 activation and provide evidence that concurrent activation of PDE3 + PDE4, operating in a synergistic manner, regulates the basal cardiac pacemaker function and provides control over normal spontaneous beating of SANCs through (PDE3 + PDE4)-dependent modulation of local subsarcolemmal Ca2+ releases (LCRs).

scholarly journals Cross-talk between cAMP and Ca2+ signalling in cardiac pacemaker cells involves IP3-evoked Ca2+ release and stimulation of adenylyl cyclase 1

2022 ◽  
Author(s):  
Samuel J Bose ◽  
Matthew Read ◽  
Rebecca A Capel ◽  
Emily Akerman ◽  
Thamali Ayagama ◽  
...  
Keyword(s):  
Guinea Pig ◽  
Calcium Release ◽  
Cardiac Pacemaker ◽  
Calcium Transient ◽  
Right Atrial ◽  
Pacemaker Activity ◽  
Intact Mouse ◽  
Atrial Tissue ◽  
Adrenoceptor Agonist ◽  
Beating Rate

Atrial arrhythmias, such as atrial fibrillation (AF), are a major mortality risk and a leading cause of stroke. The IP3 signalling pathway has been proposed as an atrial specific target for AF therapy, and atrial IP3 signalling has been linked to the activation of calcium sensitive adenylyl cyclases AC1 and AC8. Here we investigated the involvement of AC1 in the response of intact mouse atrial tissue and isolated guinea pig atrial and sinoatrial node (SAN) cells to the α-adrenoceptor agonist phenylephrine (PE) using the selective AC1 inhibitor ST034307. The maximum rate change of spontaneously beating mouse right atrial tissue exposed to PE was reduced from 14.46 % to 8.17% (P = 0.005) in the presence of 1 μM ST034307, whereas the increase in tension generated in paced left atrial tissue in the presence of PE was not inhibited by ST034307 (Control = 14.20 %, ST034307 = 16.32 %; P > 0.05). Experiments were performed using isolated guinea pig atrial and SAN cells loaded with Fluo-5F-AM to record changes in calcium transient amplitude (CaT) generated by 10μM PE in the presence and absence of 1μM ST034307. ST034307 significantly reduced the beating rate of SAN cells (0.34-fold decrease; P = 0.004), but did not result in an inhibition of CaT amplitude increase in response to PE in atrial cells. The results presented here demonstrate the involvement of AC1 in the downstream response of atrial pacemaker activity to α-adrenoreceptor stimulation and IP3R calcium release.

scholarly journals Eudragit S-100 coated sodium alginate microspheres of naproxen sodium: Formulation, optimization and in vitro evaluation / Alginatne mikrosfere naproksen natrija obložene Eudragitom S-100: Priprava, optimizacija i in vitro vrednovanje

2012 ◽  
Vol 62 (4) ◽  
pp. 529-545 ◽  
Author(s):  
Anuj Chawla ◽  
Pooja Sharma ◽  
Pravin Pawar
Keyword(s):  
Drug Release ◽  
Sodium Alginate ◽  
Naproxen Sodium ◽  
Drug Loading ◽  
Size Analysis ◽  
Scanning Calorimetry ◽  
Sem Images ◽  
S 100 ◽  
Eudragit S 100

The aim of the study was to prepare site specific drug delivery of naproxen sodium using sodium alginate and Eudragit S-100 as a mucoadhesive and pH-sensitive polymer, respectively. Core microspheres of alginate were prepared by a modified emulsification method followed by cross-linking with CaCl2, which was further coated with the pH dependent polymer Eudragit S-100 (2.5 or 5 %) to prevent drug release in the upper gastrointestinal environment. Microspheres were characterized by FT-IR spectroscopy, X-ray diffraction, differential scanning calorimetry and evaluated by scanning electron microscopy, particle size analysis, drug loading efficiency, in vitro mucoadhesive time study and in vitro drug release study in different simulated gastric fluids. Stability studies of the optimized formulation were carried out for 6 months. SEM images revealed that the surface morphology was rough and smooth for core and coated microspheres, respectively. Core microspheres showed better mucoadhesion compared to coated microspheres when applied to the mucosal surface of freshly excised goat colon. The optimized batch of core microspheres and coated microspheres exhibited 98.42 ± 0.96 and 95.58 ± 0.74 % drug release, respectively. Drug release from all sodium alginate microsphere formulations followed Higuchi kinetics. Moreover, drug release from Eudragit S-100 coated microspheres followed the Korsmeyer-Peppas equation with a Fickian kinetics mechanism. Stability study suggested that the degradation rate constant of microspheres was minimal, indicating 2 years shelf life of the formulation.

scholarly journals A complex control region of the mouse rRNA gene directs accurate initiation by RNA polymerase I.

1985 ◽  
Vol 5 (3) ◽  
pp. 554-562 ◽  
Author(s):  
K G Miller ◽  
J Tower ◽  
B Sollner-Webb
Keyword(s):  
Initiation Site ◽  
Rrna Gene ◽  
Sufficient Information ◽  
Reaction Conditions ◽  
Cell Extracts ◽  
S 100 ◽  
Initiation Reaction ◽  
Polymerase I

To determine the size and location of the mouse rDNA promoter, we constructed systematic series of deletion mutants approaching the initiation site from the 5' and 3' directions. These templates were transcribed in vitro under various conditions with S-100 and whole-cell extracts. Surprisingly, the size of the rDNA region that determines the level of transcription differed markedly, depending on the reaction conditions. In both kinds of cell extracts, the apparent 5' border of the promoter was at residue ca. -27 under optimal transcription conditions, but as reaction conditions became less favorable, the 5' border moved progressively out to residues -35, -39, and -45. The complete promoter, however, extends considerably further, for under other nonoptimal conditions, we observed major effects of promoter domains extending in the 5' direction to positions ca. -100 and -140. In contrast, the apparent 3' border of the mouse rDNA promoter was at residue ca. +9 under all conditions examined. We also show that the subcloned rDNA region from -39 to +9 contains sufficient information to initiate accurately and that the region between +2 and +9 can influence the specificity of initiation. These data indicate that, although the polymerase I transcription factors recognize and accurately initiate with only the sequences downstream of residue -40, sequences extending out to residue -140 greatly favor the initiation reaction; presumably, this entire region is involved in rRNA transcription in vivo.

Formulation and Evaluation of Mucoadhesive Floating Microspheres of Repaglinide

2021 ◽  
pp. 5673-5679
Author(s):  
S. Sivaprasad ◽  
V. Alagarsamy ◽  
M. Prathibha Bharathi ◽  
P.V. Murali Krishna ◽  
K. Sandeeep Kanna
Keyword(s):  
Controlled Release ◽  
Release Kinetics ◽  
In Vitro Release ◽  
Extended Period ◽  
Entrapment Efficiency ◽  
Sustain Release ◽  
S 100 ◽  
Eudragit S 100 ◽  
Good Flow

The main objective of the present study was to design a controlled release dosage form for an oral anti diabetic drug i.e. repaglinide employing polymers like eudragit s- 100. One of the other objective of this present study was to increase the biological half-life the drug by formulating into microspheres. The microspheres of repaglinide were prepared by solvent evaporation method by using eudragit s-100 and ethyl cellulose as polymers with different concentrations. Formulations (F1-F10) were prepared and evaluated for various micrometric properties and it was observed that though all the formulations were exhibited good flow properties, The F5 formulation exhibits higher in- vitro buoyancy time and entrapment efficiency which is considered for in- vitro and mucoadhesive studies. The FTIR results reveal that there was no interaction between the drug and the excipients. The in- vitro release profiles of F1-F5 indicated that all formulations showed controlled release over an extended period, with acceptable release kinetics. Among the all formulations F5 were considered as a promising candidate for sustain release of repaglinide.

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